PROJECT SUMMARY: Hypothermia, the only current clinical option for organ storage, allows storage times measuredinonlyhoursduringwhichtheorgandeteriorates.Thisisthemainreasonwhyhighpercentages of organs from suitable donors are not being utilized and the majority of donated organs are discarded. It also explainswhyalmostallorgansarenotoptimallydonor-recipientmatched,contributingto50%oforgans beingrejectedwithin10yearsandlife-longimmunosuppression.Werecentlydemonstratedthatreducing storagetemperatureswhileavoidingfreezingwithsupercoolingcanextendstoragetimeswithouttheaddedtissue injury from cryopreservation or deleterious phase changes, with successful transplants in rats after up to 4 days preservation. While groundbreaking experimentally, this is still insufficient in terms of global organ matching or timetoinduceimmunetolerancebymixedchimerism,whichweestimatewillrequire1weekpreservation- our overall ultimate objective. Moreover, supercooling is a non-equilibrium state with the inherent risk of ice nucleation and freezing at subzero temperatures. The innovation we propose here is to use established physicalprinciplestoenableequilibriumsub-coolingthatisstableatsubzerotemperaturesirrespectiveof samplevolumeortimeofstorage.Weproposetodevelopanon-toxicsolutiontobankwholehumanorgansthat can enable global organ matching, increase the use of marginal donor organs, and revolutionize organ transplantation. Our approach will develop a nature-inspired cocktail that enables stable human organ subzerononfreezingstorage(intherangeof-5to-20C).Suchstrategiesareusedinnaturetosurviveweeks attemperaturesaslowas-14Cinastateof?suspendedanimation,?withthewholeanimal,includingeverysingle organ,being?banked?withoutinjury.Further,werecentlydemonstratedthatacombinationofmachineperfusion and subzero nonfreezing storage at -6C tripled viable preservation times of banked whole rat livers for transplantationwith100%survival.Basedonthispreliminaryworkweconceivedatwo-prongedapproachinwhich our first generation supercooling protocol is augmented with cryostasis protocols designed using new equilibrium calorimetrydataforarangeofnovelcryostasiscocktailstoremainunfrozenathighsubzerotemperatures.Thisis achieved by restricting cooling to temperatures above the equilibrium melting curve defined in a phase diagram. Thesenewsolutionsandprotocolswillthenbeevaluatedusinghumancellmodelsbeforeassessingthiscombined approachinratstudiesandtestingwithtransplants.FinallywewillpreservewholehumanliversinaSZNFstateas proofofconcept. OurmilestoneinthisR21studyisdemonstrationofthisaugmentedprotocolinhumanliversat3 days,whichwouldrepresenta>5-10foldincreaseovercurrentclinicalpractice.Infollow-upstudieswe willextendthislimitto1weekandtestwithporcinesurvivaltransplants.